What is Level Switch : Working, Types & Its Applications

The utility water tanks in power plants and factories need to observe and control the water levels. So, a level meter and a level switch are used to detect & measure different materials like powder, liquids & granulated materials within vessels, tanks & plumbing. This type of switch fits in any kind of application or product. So these switches are utilized as a monitoring control, measurement device, and warning alarm like when to turn on or off a device.


Level switches are available in two categories like point & continuous where point level mainly includes optical, vertical, ultrasonic & horizontal float, and constant level type mainly includes ultrasonic, capacitive & submersible. The type of level switch is determined through the measurement types & the environmental conditions. So this article discusses an overview of a level switch – working with applications.

What is Level Switch?

A level switch definition is; a switch that is used to detect levels of liquid otherwise interfaces in between liquids. The measurements of liquid levels are simply specified through the action of electrical switching. These switches can be utilized as either control switches or an alarm device by switching ON/OFF of a load. These switches are very special because they have a switched output and are either solid-state or electromechanical and are either normally closed or normally open.

Level Switch
Level Switch

Working Principle

The level switch working principle is; that once the float moves by the raise within the level of water then the output contact will be changed & it specifies the position of the water level.

For instance, once a tank is supplied with water, then it overflows. So to overcome this overflow, a level switch is connected to the top of the water tank. Once the water strokes the switch, then it gives an outputs signal to maintain the water flow from overflowing the water tank. Alternatively, once the liquid or water level reduces when the water is discharged, then a switch is utilized to avoid draining the tank.

Level Switch Wiring Diagram

The liquid level switch circuit diagram is shown below. This circuit is designed with some passive components, three BC107 transistors, a couple of relays & a diode. This is a level sensing circuit designed using minimal components.

Level Switch Wiring Diagram
Level Switch Wiring Diagram

This circuit is connected as per the diagram shown above. In the above circuit, adjust the resistor ‘R1’ by placing the probes within the water tank to turn ON the K1 relay. After that, take out two probes from the water tank & observe the K1 relay turned OFF. During this time, the opposite will be occurring within the K2 relay. If you cannot get the setting change the ‘R1’ resistor with a 500K POT & do again the process.
The main problem of this circuit is the rust of probes while DC is used. Anyhow, this setup will run problem-free for a minimum of one year.

Working

This simple level circuit works by turning ON one relay & turn OFF another relay once the level of fluid exceeds the set limit.

Whenever the water level contacts the probes then a positive supply is given to the base terminal of the Q1 transistor throughout the fluid. So this makes the Q1 transistor ON. The base terminal of the Q2 transistor is connected to the collector terminal of Q1& base terminal of the Q3 transistor is connected to the collector terminal of the Q2 transistor. Thus, the Q1 transistor will be turned on & Q2 transistor will be turned OFF. So the ‘K2’ relay will be turned OFF & ‘K1’ relay will be turned ON.

These two relays work based on the water level. The relays contacts like OP1 & OP2 are mainly used  as an control for any device like pumps, motors, alarms, lights, solenoid valves, etc. Once the level of water drops, then the K2 relay will be turned ON & K1 relay will be turned OFF.

Level Switch Vs Level Transmitter

The difference between the level switch and the level transmitter includes the following.

Level Switch

Level Transmitter

A level switch is also called a level sensor. Level transmitter is also known as level gauges.
This switch is suitable wherever very high or very low levels need to be calculated. A level transmitter is suitable where the precise liquid level needs to be calculated.
These are expensive as compared to transmitters. These are inexpensive as compared to switches.
As compared to load transmitters, these are not reliable & robust. These transmitters are more reliable & robust.
The information available on the switch is less as compared to a transmitter. The information available on this is more as compared to a switch.

Level Switch Types

There are different types of level switches including ultrasonic, inductive, thermal, magnetostrictive, capacitance, potentiometric, hydrostatic, diaphragm, optical, tilt, paddle, rod, conductivity, displacement, tuning fork, potentiometric, capacitance, nuclear, rotating, and paddle. Some of them are discussed below.

Ultrasonic Level Switch

These types of level switches are mainly used in industrial processes for detecting low & high liquid levels. The measurement of liquid level can be done by transmitting ultrasonic range signals thus it works by sending ultrasonic signals in between two crystals. Here, the transmitter & receiver could be within a similar probe otherwise on the reverse face of the water tank. These switches are used for both solid & liquid material-based applications.

Ultrasonic Level Switch
Ultrasonic Level Switch

Inductive Level Switch

The inductive level switch is simply considered an electronic circuit, which is used to determine the changes in inductive reactance. To attain this, the conductive fluid should cooperate with the magnetic field. This switch is most frequently used in harsh environments because of fewer moving parts & sealed probes.

Inductive Type
Inductive Type

These switches can be observed in industrial applications. These types of switches can also be used within solids & conductive liquids; so they can be used on the interface between the conductive and non-conductive liquids.

These are non-contact switches that simply react to a targeted material once the material comes within the detecting field.

Inductive Switch in a Oscillator Resonant Circuit

An oscillator resonant circuit uses an open core coil to generate a concentrated high-frequency electromagnetic field that comes from the surface of the sensor. If a material moves the target area, then eddy currents are generated.

Oscillator Resonant Circuit
Oscillator Resonant Circuit

Once the detection is made, then the oscillating unit amplitude reduces & the oscillator is attenuated. The oscillating unit’s lower amplitude transmits a signal to the electronic circuit that alters the switching condition of the inductive level switch.

Thermal Level Switch

Thermal level switches are mainly used to detect the variation within the temperature of the liquid & vapor space. This switch includes a thermistor or heated thermal resistor that is heated continuously. This switch is activated once there is a drop in the thermistor’s heated temperature.

Thermal Level Switch
Thermal Level Switch

In this type of switch, a thermistor detects the liquid’s surface, then liquid level measurement can be done with a thermistor. The measurement is done by the thermistor based on the difference in the thermal conductivity of liquid & air.

Since heat dispersion within liquids is higher as compared to air or gas, and then the resistance of the thermistor probe will be changed sharply once it is placed within a fluid. These switches are very accurately up to 1000° C temperature.

Capacitance Level Switch

A capacitive level sensor is an electronic device that measures the height of a fluid surface. The sensor consists of a conductive plate, which is mounted on a movable arm (the probe). The probe has a capacitance value. As the probe approaches the surface, the capacitance between it and the surface decreases. This change can be measured and converted into an accurate measurement of the height of the surface above the probe.

The most common application for capacitive level sensors is industrial measurement, where they are used to measure liquid levels in storage tanks or open-top vessels. A capacitive level sensor can also be used to measure other fluids, such as air pressure or temperature.

Capacitance Type
Capacitance Type

Magnetostrictive Level Switch

These types of level switches detect the level of a liquid by sensing the level of the magnet within the float & transmit the data back toward the control system. This switch includes buoyancy, electronics & magnetostriction to measure liquid levels. A liquid float moves up & down because of its buoyancy that is mounted on the stem of the level transmitter.

Magnetostrictive Type
Magnetostrictive Type

Potentiometric Level Switches

These are continuous level switches that are used within metal containers. A measuring tube with low resistance is submerged in a conductive fluid-like glue or paste. A high-frequency current is transmitted throughout the tube. So a voltage reading can be taken from the space between the probe & the wall of the tank, which is transmitted to an amplifier. The transmitted reading is simply proportional to the level of the tank.

Potentiometric Type
Potentiometric Type

Hydrostatic Level Switches

Hydrostatic level switches are threshold contact that contains a pressure switch or pressure sensor placed in a solid-state NPN or PNP switch. All liquids are influenced by gravity and produce hydrostatic pressure, which is similar to the weight of a solid object. With liquids, it is possible to measure the weight of the liquid at its level. The weight of the liquid at different levels is proportional to a specific level.

Hydrostatic Type
Hydrostatic Type

Hydrostatic level switches are continuous level measurement switches mounted on the side of a container using a flange, threaded port, or sealed clamp.

Diaphragm Switch

A diaphragm level switch is mainly used to measure the change within pressure caused by the level of the material increasing or decreasing. Whenever the level increases, then air pressure gets high & the diaphragm face drops under the force, which actuates a micro switch. Once the force gets lower, the diaphragm comes back to its early position. These types of switches have an electrical contact output & used in a wide range of industries.

Diaphragm Switch
Diaphragm Switch

Optical Level Switch

These switches simply use the reflection concept within a prism & it is utilized for high pressure & temperature applications. This switch can be used as a point level detector as well as a continuous measurement level switch for liquids & solids. The reflected light is transmitted to the sensor’s receiver & it is refracted through the liquid being observed. The essential components of this switch mainly include an IR LED & a light receiver.

Optical Type
Optical Type

They sense the changes within the level using IR light transmitted from an IR diode. Light is transmitted to a cone-formed prism. Once the cone is over the liquid, then it is reflected by the detector. Similarly, the light won’t be reproduced if the cone is under the liquid level. Whenever the detector does not get returned light, then is triggered an alarm.

Tilt Level Switch

These types of switches are called high-level indicators that are balanced on a cable over the material. When the media increases & contacts the tilt switch, then it simply tilts to the side. These types of switches are mainly designed to avoid overflow of bins & control liquid levels within open pipes. These switches are mainly used for above or below loads in conveyor systems.

Tilt Level Switch
Tilt Level Switch

Paddle Level Switch

A paddle level switch includes an electric motor that turns a metal paddle slowly. Once the material within the container attains the paddle level, then the material will put a load on it. A torque switch is connected to the electrical motor of the switch and it triggers whenever a plenty amount of torsional pressure is located on the paddle. A paddle switch is mainly used to perform the detection of point level within dry bulk materials.

Paddle Level Switch
Paddle Level Switch

Rod Level Switch

These level switches include a stainless steel rod that oscillates or vibrates at a precise frequency & is power-driven through an electronic circuit. Once the media attains the vibrating rod, the vibrations will stop & gives an alert to the control system. These are point form switches that are used as low & high-level indicators otherwise for detecting plugged chutes.

Rod Level Switch
Rod Level Switch

Conductivity Level Switches

These switches include highly sensitive & complicated sensors which help in recording small changes within the level of a fluid. These switches have conductive probes that are insulated electrodes apart from their tips to keep away from electrical bridging. The probes of this switch simply work when the electrical resistance changes between them through two electrodes where one is the reference electrode & other one is the level control electrode. The process of conductivity electrodes detects the resistance level whenever they are enclosed within the medium.

Conductivity Level Switches
Conductivity Level Switches

Displacer Level Switch

This level switch includes a detecting element like weight or displacer, which is heavier as compared to the liquid, balanced from a spring. Once the liquid makes contact with the displacer, then buoyancy energy is formed to cause a change in the weight of the displacer, in turn, the spring looks for a new balance position to turn the attraction sleeve to the magnet field. So the magnet will go upwards in the pressure tube to activate the switching mechanism, because of this working principle, it is used in wide switching differentials.

Displacer Type
Displacer Type

Calibration of Level Switch

The calibration of the level switches is necessary for ensuring their reliability & accuracy. So, the incorrect calibration can cause faults within results otherwise damages the switch.

  • The steps involved in pressure switch calibration are discussed below.
  • Fill the process into the chamber up to the level switching mark.
  • The level switch contacts must be adjusted.
  • The level switch must be disconnected or depressurized for security.
  • Connect the pressure calibrator to the input of the switch
  • Connect the device to calculate the output condition of the switch.
  • Across the operation point, move liquid pressure very slowly, until the output of the switch toggles and record the operation pressure.
  • Move pressure slowly in the direction of the return point, until the switch position toggles and record the return pressure.
  • Repeat the steps if required and detach the test equipment
  • Return level switch back to service.

Advantages and Disadvantages

The advantages of the level switch include the following.

  • These switches are economical so used for monitoring, controlling & changing liquid levels.
  • Each switch needs raw materials in the manufacturing procedure of control to keep away from waste.
  • The bulk storage control & liquid materials helps in avoiding waste from spillage & overflows.
  • A level switch that is programmed properly can turn on a pump or valve to avoid losses & control overflow.
  • By using these switches, money can be saved.
  • These types of switches are capable of providing correct data on time to a computer without activating or starting another device.
  • These switches are reliable and versatile.
  • Installation is simple.
  • These switches are solid & handheld.
  • Its design is compact.
  • Different kinds of switches available to mount for the top, bottom, and side
  • The conductivity or Dielectric constant of liquid will not influence its operation.

The disadvantages of the level switch include the following.

  • Moving parts are vulnerable to damage, wear, and tear, and clogging.
  • Float actuation mainly depends on liquid contact
  • Turbulence within the liquid may cause the float to shift.
  • Sticky or Thick fluids may avoid the liquid float from moving.
  • It needs regular maintenance.

Applications

The applications of the level switch include the following.

  • These switches are mainly used for measuring substances in a container otherwise in their natural state like rivers.
  • These switches are used in different industries like water treatment, oil plants, paper & pulp, handling waste material industries, power generating plants, beverage & food manufacturing factories, etc.

Thus, a level switch is a mechanical or electrical device, used to measure the liquid level. These types of switches are very essential in production operations & are utilized in harsh conditions in extreme pressure, vibrations & temperatures. These switches are sued for controlling, monitoring, and changing the levels of fluids, bulk materials otherwise liquids. Here is a question for you, what is a level transmitter?

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